This project is designed primarily to investigate three changes in the E. coli cell surface that occur after bacteriophage T5 infection. The first is the appearance of a major new membrane protein very early after infection. This protein is the product of the Al gene of T5 and is required for injection of the whole T5 DNA molecule. This protein is being purified by antibody affinity chromatography for further characterization. A later change in the cell envelope that occurs after infection is the inactivation of the receptor for T5 on the cells' surface. A biochemical-genetic study of this reaction is in progress to determine the mechanism of receptor inactivation and the genes controlling this process. The third change occurs under the influence of the Col Ib plasmid. When cells containing this plasmid are infected with T5 the cell membrane begins to degenerate causing the infection to be abortive. The mechanism whereby this occurs is under investigation.